High quality printing of a web, such as a continuous paperstrip, in a conventional multi-roll printing apparatus can only be achieved when tight control over the operating parameters is maintained. Should this control be lacking or should a transient malfunction occur, then a defect will be visually apparent. Such defects include out-of-registration print, hickie marks, splice marks, blanket wash marks and the like. Those portions of the web having these defects are not suitable for distribution to the customer and must be separated from the remaining good portions.
Conventional printing presses operate at high rates with speeds of up to 300 to 1000 revolutions per minute, thereby rapidly printing large quantities of paper. Those skilled in the art realize, therefore, that a defect, if not immediately corrected, can rapidly ruin a tremendous amount of paper, at a resultant large cost. These defects, such as out-of-registration print and hickie marks, are apparent only by selective inspection of the material (pulling a sample out and examining for defects) coming from the press. Correction takes time and requires clear-up of the print rolls after removal of a piece of dust, paper etc. caught on the rolls. Thus, the operator, in correcting the defect, causes a transient defect. Shut down and start up of any press causes a great deal of time loss and expense and, therefore, defect correction is normally done while the press is running, even though there are some waste losses.
Additionally, a defect is caused by the splice created by the splicer which joins the end of a spent roll to the end of a new roll. This splice joint creates an undesirable transient distortion in the print image. Another source of defect results from the periodic cleaning or washing of the print cylinders.
In view of the above, it can be appreciated that there is a need for a method and apparatus which permits defective portions of a printed web to be marked for ease in inspection without requiring selective sampling. The defective portions then can be easily separated from the good portions with a minimum of waste while permitting the press to continue to operate. Dalin, U.S. Pat. No. 3,289,835, discloses a marking apparatus for a newspaper printing machine wherein the front page of a completed and folded defective newspaper is marked. The solution suggested by Dalin is not satisfactory for high speed printing presses. Dalin fails to take into account the defective portion in the press and the time required for that portion to pass through the press. Also, Dalin involves inspection after all operations have been completed.